I can say that it hasn't got anything to do with my bowels/intestines - I had/have a lot of those cramps for so many years, so I know that sort of pain very well...
Excuse me, maybe TMI, but well, if we can talk about poop and enema's and so on, why not: even my anus hurts really bad when I have those cramps, like the muscles around it, not the intestine itself. Sorry guys... I feel a bit embarassed to talk about it... The cramping can last for a while, but when peaking it affects that area also - really painful... There's like a general cramp that lasts, but with 'waves' of really very intense pain.